Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.58	10.381%	$41.4812	$41.48	$41.50	$41.50
Purchase #2	$88.87	12.508%	$99.9859	$99.99	$100.00	$100.00
Purchase #3	$93.26	7.330%	$100.096	$100.10	$100.10	$100.10
Purchase #4	$134.30	3.765%	$139.3564	$139.36	$139.35	$139.40
Purchase #5	$7.37	4.391%	$7.6936	$7.69	$7.70	$7.70
Purchase #6	$43.28	9.787%	$47.5158	$47.52	$47.50	$47.50
Purchase #7	$29.63	10.610%	$32.7737	$32.77	$32.75	$32.80
7 purchase totals =	$434.29		$468.9026	$468.91	$468.90	$469.00